1. Field of the Invention
This invention relates to a primer composition useful for bonding adherends such as silicone elastomers to substrates such as coated metals.
2. Prior Art
Among conventional building exterior wall materials, metal members surface coated with paint compositions of fluorine resin, urethane resin or acrylic resin systems are widely utilized. Often sealants such as room temperature vulcanizable silicone elastomers of the condensation type are jointed to these coated metal members. It is also a common practice to join room temperature vulcanizable or heat curable silicone elastomers to polycarbonates, polybutylene terephthalate (PBT) resins, ABS resins and acrylic resins which are commonly used in electric and electronic applications. The recent spreading use of plastic materials in a wider variety of industrial fields raises many demands. It is one of such demands to join silicone elastomers to plastic substrates.
Silicone elastomers, however, do not provide a sufficient bond to coated metals, polycarbonates, PBT resins, acrylic resins, and other plastic materials. It is then a common practice to previously coat substrates with primer compositions based on silanes or hydrolysis condensates thereof before silicone elastomers are joined to the substrates.
A number of primer compositions have been proposed for joining silicone elastomers to substrates. For example, Japanese Patent Application Kokai (JP-A) No. 32030/1977 discloses a composition comprising a tetraorganotitanate, an epoxy group-containing alkoxysilane, an unsaturated bond-containing organic silicon compound, a platinum compound, an organic solvent-soluble polymer, and an organic solvent. Japanese Patent Publication (JP-B) No. 2107/1986 or U.S. Pat. No. 4,332,844 discloses a composition comprising an alkoxy group-containing organic silicon compound, an organic titanium compound, and a hydrosilyl group-containing organic silicon compound. These primer compositions fail to achieve a satisfactory joint in some cases. In addition, the demand for a long-lasting joint is increasing. There is a need to have a primer composition having improved bond ability and bond durability.